Strength of orthogonally reinforced plastics in uniaxial tension

Failure conditions are proposed for an orthogonally reinforced plastic in uniaxial tension at an arbitrary angle to the directions of reinforcement. The failure conditions are formulated for the case when the strength of the bond between the resin and the reinforcement is greater than the strength of the resin. The strength of the resin, which is in a volume state of stress, is determined by an energy criterion.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 629–633, July–August, 1973.     

The effect of glass fiber inelasticity on the long-term strength of reinforced plastics subject to uniaxial tension along the fibers

Relationships are presented for determining the long-term strength of reinforced plastics subject to uniaxial tension by a constant load directed along the fibers; these relationships are based on the rheological characteristics of the components of the plastics. The proposed expressions agree quite well with experiment. Treatment of the experimental data by mathematical statistics showed that the relative strain at fracture remains constant; it does not depend either on the relative reinforcement content or on the applied load (i. e., on the time to fracture).Mekhanika Polimerov, Vol. 3, No. 4, pp. 719–725, 1967     

Short-time strength of reinforced plastics in uniaxial compression

The short-time compressive strength of one-way and two-way reinforced plastics compressed in the direction of the axes of elastic symmetry has been theoretically and experimentally investigated with allowance for the mechanical properties of the components and the orientation of the fracture (shear) plane.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 621–628, July–August, 1969.     

Continuity condition for orthogonally reinforced plastics in tension

The proposed continuity condition is based on the hypothesis that the time dependence of the strength and limiting strain of the resin is determined by the limiting value of the specific work done by the stresses. The case when the reinforcement is elastic and the rheological properties of the resin are described by a linear differential equation is considered.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 844–852, September–October, 1968.     

Creep and long-time strength of unidirectional reinforced plastics in compression

An attempt is made to predict the creep and long-time strength of unidirectional reinforced plastics in compression in the direction of the reinforcement from the properties of the components. The reinforcement is assumed to be elastic, while the resin is described by a Boltzmann-Volterraintegral equation with fractional-exponential Rabotnov kernel. Experimentally obtained creep and long-time strength curves are presented for unidirectional reinforced plastics.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 830–835, September–October, 1970.     

Propagation of elastic waves along the fibers in oriented glass-reinforced plastics

The dispersion equation is derived for axisymmetric (longitudinal and torsional) normal vibrations in oriented glass-reinforced plastics. The low-frequency case is examined in detail. The frequency limits of applicability of the method of substituting a homogeneous medium for the composite (GRP) are estimated. The dependence of the vibration propagation velocity on glass content is calculated.Leningrad Zonal Scientific-Research Institute of Experimental Design of Public and Residential Buildings. Translated from Mekhanika Polimerov, No. 6, pp. 976–983, November–December, 1973.     

Deformative characteristics of plastics reinforced with high-modulus anisotropic fibers

The independent elastic constants of plastics unidirectionally reinforced with transversely isotropic fibers have been determined. It has been assumed that the distribution of reinforcement in a transverse section of the plastic is regularly rectangular or hexagonal. To determine the transverse elastic modulus and the shear modulus in the plane of reinforcement, a constancy-of-plane-sections hypothesis was used. Values of deformative characteristics determined by the assumed calculational dependences have been compared with the experimental ones for plastics reinforced with graphite fibers.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 631–639, July–August, 1972.     

Creep of unidirectional glass-reinforced plastics based on new types of fibers

Theoretical and experimental compressive creep relations for a unidirectional glass-reinforced plastic based on hollow fibers are presented. The agreement between the theoretical and experimental data is shown to be satisfactory. The effect of fiber capillarity on the creep process is unimportant.All-Union Scientific-Research Institute of Glass-Reinforced Plastics and Fiber Glass, Moscow; Institute of Mechanics of Machines and Polymeric Materials, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Mekhanika Polimerov, No. 4, pp. 747–750, July–August, 1971.     

Strength and deformability of reinforced polymers in tension normal to the fibers

The strength and deformability of reinforced polymers in tension across the fibers is investigated. It is assumed that the polymer deforms as an ideal elastoplastic body. Relations are obtained for the nature of the deformation of the polymer between the fibers and the strength and deformability of the composite with allowance for the structural distribution of the components. Theoretical stress-strain diagrams are presented for composites with different reinforcement densities and resin elasticities. The theoretical values of the strength and deformation of reinforced polymers with the load applied across the fibers are compared with the results of experiments on model specimens of epoxy-Thiokol polymers.Leningrad Mechanical Institute. Translated from Mekhanika Polimerov, No. 4, pp. 682–687, July–August, 1970.     

Effect of curvature of the fibers on the elastic properties of unidirectionally reinforced plastics

An approximate method is proposed for determining the reduced elastic constants of reinforced plastics (glass-reinforced plastics) with allowance for the curvature of the reinforcing fibers. All the conclusions relate to plane stress. The results of model tests are presented as confirmation of the theoretical conclusions.Mekhanika Polimerov, Vol. 3, No. 5, pp. 858–863, 1967     

Stresses in plastics reinforced with anisotropic fibers and subjected to transverse normal loading

The question of the stress distribution in plastics reinforced with anisotropic fibers and subjected to transverse normal loading is considered. The stresses in the components are determined by the methods of the theory of elasticity using stress functions. The theoretical relations obtained are used to construct diagrams showing the distribution of the tangential, radial, and shear stresses in the composite and the isoclines of the concentration coefficient for a carbon-reinforced plastic. The results obtained for the carbon-reinforced plastic are compared with the analogous results for a glass-reinforced plastic.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 244–252, March–April, 1973.     

Creep of plastics with spherical inclusions

A new variant of the theory of creep of plastics with spherical inclusions or pores is proposed on the basis of approximate equations for the integral parameters and the Volterra principle. Rabotnov's theory of viscoelasticity is used to describe linear creep of the matrix. The remaining components of the composite are assumed to be elastic. The complete system of operator equations of the linear viscoelasticity of plastics with spherical inclusions is obtained on the basis of the hypothesis of elastic deformation of the composite and hydrostatic pressure. Sample calculations are performed. A. A. Blagonravov Institute of Mechanical Engineering, Russian Academy of Sciences, Moscow. Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 668–675, September–October, 1996.     

Structural stresses in reinforced plastics

The safety parameters at any given point of a microinhomogeneous medium simulating the structure and properties of reinforced plastics are determined by solving the statistical boundary value problem. The results are illustrated in relation to randomly reinforced glass laminates.Mekhanika Polimerov, Vol. 3, No. 3, pp. 413–420, 1967     

Deformation characteristics of glass-reinforced plastics in tension

It has been shown experimentally with reference to two glass-reinforced plastics (reinforced with fabric and rovings) that at stresses above the break on the stress-strain curves the ratio of the transverse strains ₃ developing at right angles to the layers and the longitudinal strains ₁ changes. Raising the test temperature of the glass laminate intensifies this change.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 5, No. 2, pp. 373–375, March–April, 1969.     

Experimental evaluation of the effect of prestressing the fibers in two directions on certain elastic characteristic of woven-glass reinforced plastics

The effect of prestressing the reinforcing fibers in either of two mutually perpendicular directions on the elastic characteristics of woven-glass reinforced plastics has been experimentally investigated. It is shown that an increase in the elastic characteristics in the prestress direction is accompanied by a decrease in the direction at right angles. Applying the same prestress in both directions considerably improves the moduli of elasticity (E_x, E_y). The possibility of using Bolotin's theory [1] and the relations proposed in [4, 6] to estimate the effect of regular distortions of the fibers on the elastic moduli of woven-glass reinforced materials is examined.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 859–863, September–October, 1968.